Shear-enhanced magnetic nanoparticle chain formation in ferrofluids

In this work, we propose to enhance magnetic particle (MP) chain formation in ferrofluids using shear flows. Through modified dissipative particle dynamics simulations, we study the dynamics of MP chain formation, including the mean MP chain length and the number of chains under various MP volume fractions and shear rates. It is found that shear flows greatly accelerate the formation of MP chains, especially at high volume fractions. A strong shear, however, can impede the formation of long chains. The maximum mean length of the MP chains is 182% to 324% larger than those without shear when the volume fraction of MPs changes from 5% to 30%. The effects of shear rate and volume fraction in MP chain formation are explained by calculating the diffusion coefficients of MPs and the base fluid and the energy barrier for MP chain formation. Moreover, shear flows do not significantly increase the temperature of the ferrofluid, making it an ideal method for enhancing MP chain formation.